69D and 769D Off-Highway Truck and 771D Quarry Truck Air System and Brakes Caterpillar

(1) Air tank check valves

(2) Air relief valve for primary air tanks

(3) Primary air tanks

(4) Drain valve

(5) Front brake inverter valve

(6) Brake air relay valve for the front brakes

(7) Brake air relay valve for the rear brakes

(8) Brake air system pressure protection valve

(9) Brake air relay valve for the Automatic Retarder Control (ARC)

(10) Air compressor with an air compressor governor

(11) Air dryers with air relief valves

(12) Parking and secondary brake valve

(13) Brake master cylinder (front)

(14) Brake master cylinder (rear)

(15) Air horn

(16) Front brake air control valve

(17) Front brake air ratio valve

(18) Air system pressure protection valve

(19) Service brake air control valve

(20) Air suspension seat

(21) Remove these lines when the Automatic Retarder Control (ARC) is installed. Also remove this pressure switch.

(22) Air horn solenoid

(23) Retarder air control valve

(24) Secondary brake air control valve

(25) Parking brake air control valve

(26) Secondary brake inverter valve

(27) Automatic Retarder Control (ARC) valve (attachment)

(28) Secondary air tank

(29) Cab wall

(A) This is the brake cylinder overstroke limit switch (overstroke switch). The overstroke switch is normally closed. The overstroke switch opens when the pistons in the master cylinder travel too far. A brake overstroke condition can result from low brake fluid level, air in the brake hydraulic circuit, leakage in the brake hydraulic lines, and master cylinder piston seal leaks. An indicator will come on in the cab and the alarm will sound. Do not operate the machine until the cause for the overstroke has been corrected.

(B) This is the secondary brake and parking brake pressure switch. This pressure switch is normally open. The pressure switch is closed by air pressure when the parking brakes or secondary brakes are released. When this pressure switch is open, this pressure switch signals the Power Train Electronic Control Module (Power Train ECM) to allow rapid shifts.

(C) This is the brake air pressure sensor. The brake air pressure sensor monitors brake air pressure. The operator will be alerted to a condition of low air pressure.

(D) This is the manual retarder pressure switch. This pressure switch is normally open. This pressure switch is closed when the retarder air control valve is applied. This switch operates the indicator in the cab.

(E) This is the service brake and retarder pressure switch. This pressure switch is normally closed. This pressure switch is opened by air pressure when the service brakes, the retarder, or the Automatic Retarder Control (ARC) are applied. When this pressure switch is open, the pressure switch signals the Power Train ECM in order to allow the transmission to perform rapid shifts. The Power Train ECM also indicates that higher engine rpm is needed for upshifts or for downshifts of the transmission when this pressure switch is open.

(F) This is the stop lights pressure switch. This pressure switch is normally open. This pressure switch is closed by air pressure when the service brakes, the retarder, or the Automatic Retarder Control (ARC) are applied. When this pressure switch is closed, this pressure switch activates the stop lights.

(G) This is the Automatic Retarder Control pressure switch. This pressure switch is normally closed. This pressure switch is opened by air pressure in order to indicate that the Automatic Retarder Control (ARC) is operating. The pressure switch verifies that air pressure is being provided through the Automatic Retarder Control valve.

(H) Standard air lines

(16) Front brake air control valve

(1) Air tank check valve

(28) Secondary air tank

(E) Service brake and retarder pressure switch

(22) Air horn solenoid

(26) Secondary brake inverter valve

(17) Front brake air ratio valve

(18) Air system pressure protection valve

(B) Secondary brake and parking brake pressure switch

(19) Service brake air control valve

(27) Automatic Retarder Control (ARC) valve (attachment)

(D) Manual retarder pressure switch

Top view of the air lines on the platform beside the cab

(1) Check valve for the primary air tanks

(2) Air relief valve for primary air tanks

(3) Primary air tanks

(5) Front brake inverter valve

(6) Brake air relay valve for the front brakes

(7) Brake air relay valve for the rear brakes

(8) Brake air system pressure protection valve

(9) Brake air relay valve for the Automatic Retarder Control (ARC)

(13) Brake master cylinder (front)

Rear view of the air lines on the platform beside the cab

(2) Air relief valve for primary air tanks

(3) Primary air tanks

(5) Front brake inverter valve

(6) Brake air relay valve for the front brakes

(7) Brake air relay valve for the rear brakes

(8) Brake air system pressure protection valve